Primer bulb pulling air but not the usual suspects.

[jarrick]

Got an old Tanaka ECS 3351b (33cc) and the primer/purge bulb gets a lot of air coming in from somewhere.

Replaced all the tubes with new clear ones and the tube going from the carb to the bulb gets a lot of bubbles going through and hardly any petrol.

The saw runs but not as well as it should (though that might be a tuning issue).

I've recently cleaned the carb and put new gaskets and diagrams etc, and all the screws are done up tight.

I even swapped the carb with the one in my spare saw - and that was even worse.

The primer bulb is new and tested ok.

 

Any ideas?

 

[openspaceman]

If the carb you tried was off another working saw and worked well then no, unless the tubes are on the purge bulb the wrong way round.

 

The problems I have had with air being pulled into the purge valve have been worn/leaking throttle enriching pump ( and this cannot be completely deleted, @bmp01 fixed it with a blocking plug that still allowed fuel in the purge circuit ) and the main check valve leaking. In the latter case I think it was someone poking a wire through it or blasting it with compressed air.

[Muddy42]

As above are you sure the primer is connected the right way?  Its short line from (normally the top of the) carb, long line returning to the fuel tank. The fuel line goes from the fuel tank to the bottom of the carb.

 

If the lines are clear, you should see where the bubbles start from?

 

Are you sure the carb was assembled in the correct way? If any of the diaphragms ripped, it could benefit from a carb kit.  You can pressure test a carb, but do it gently to avoid breaking stuff. You don't need a pressure tester for this, if you blow with your mouth on the fuel line you get an idea if the pressure is dropping.

Edited 17 hours ago by Muddy42